Glower lamp and process



Feb. 25, 1969 R. s. CARTER v 3,

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United States Patent 3,429,832 GLOWER LAMP AND PROCESS Ralph E. Carter, Colonie, N.Y., assignor to General Electric Company, a corporation of New York Filed May 31, 1966, Ser. No. 554,022 US. Cl. 252-520 Int. Cl. H01!) 1/02; H01j 17/20 2 Claims ABSTRACT OF THE DISCLOSURE This invention relates to an improved glower lamp and to a process for manufacturing the lamp and more specifically to a lamp utilizing a refractory metal oxide glower element which requires no auxiliary heat before operation can be initiated.

The type of glower lamp with which this invention is concerned includes an electrically resistive glower element that is connected to a source of electricity and compositionally is composed of refractory metal oxides. One of the mode widely adopted metal oxide compositions is zirconia containing either yttrium oxide or calcium oxide or both. It should be pointed out that some hafnium oxide is present since zirconium oxide almost always contains this material as an impurity. Since the device operates by virtue of the passage of electricity through the resistive metal oxide glower element, it has been necessary that this element be heated to a temperature on the order of about 1000 C. before it became conductive enough to pass electric current and generate radiation. This feature has, therefore, required that glowers of the Nernst type have present an auxiliary heater to elevate the temperature of the glower element to the point where operation to produce radiation can be initiated.

It is a principal object of this invention to provide an improved glower for generating radiation in which no auxiliary heater is needed.

It is an additional object of this invention to provide a process for producing an improved glower-type radiation generator.

Other objects and advantages of this invention will be in part obvious and in part explained by reference to the accompanying specification and drawings.

In the drawings, the figure is a side elevation of an improved generator according to this invention with parts broken away to more clearly illustrate the construction.

Broadly, the improved glower lamp or generator of this invention comprises a glower element constructed of a refractory metal oxide, means connecting the glowerelement to a source of electricity and a sealing container enclosing the glower element and defining an operating chamber which isolates the glower element from the surrounding environment.

The process for producing the improved generator comprises heating the glower element by any suitable means to a temperature of at least about 1000" C. while maintaining the element in an oxygen-free environmet that is non-reactive with the oxides from which the element is composed. After the element has been brought to this temperature, direct current is passed through it for a period of time sufiicient to electrolyze the element, thereby lowering its electrical resistance. The element must thereafter be maintained in an oxygen-free environment during operation if the improvement in electrical conductivity is to be retained and generation of radiation initiated simply by passing current through the element starting at room temperature. The element may be exposed to 0 containing atmospheres at room temperature and sulfer no harmful effect by way of an increase in resistivity.

The construction of the improved glower can best be seen by referring to the drawing wherein the numeral 10 designates a glower element constructed of a refractory metal oxide. The composition of element 10 is normally one containing from about 48 to 93 mol percent zirconia combined with from 10 to 20 mol percent calcium oxide or from about 7 to 52 mol percent yttrium oxide. The preferred composition is from 8 to 10 mol percent yttria, balance substantially all zirconia, except for the small percentage of hafnium oxide which is usually present as an impurity in the zirconia. Combinations of calmium and yttrium oxide can be added to the basic zirconium oxide if desired but no particular advantage is obtained by doing so.

The glower element 10 is supported within a sealed container 11 by means of any suitable electric insulating supports 12 that are secured at one end to the glower element 10 and at the other to the sealed container 11. Means such as wires 15 are electrically connected at specified points to glower element 10 and extended outside of container 11 for connection to a suitable source of electricity.

The sealed container 1'1 defines an operating chamber 16 isolated from the surrounding environment and this chamber contains an oxygen-free environment which is nonreactive with the material from which glower element 10 is constructed. Suitable environments include, for example, the noble gases, viz. helium, neon, argon, krypton and xenon, as well as vacuum. Generally, gases of commercial grade are suitable for use in the improved glower of this invention and although slightly higher oxygen contents can be tolerated, not more than about 10 ppm. 0 content in the gas is preferred.

It was indicated previously that the glower of this invention for the first time made it possible to construct and operate a Nernst-type glower without the necessity of utilizing an auxiliary heater to first raise the temperature of the glower element. This result is achieved by means of a novel process which includes as an important step that of heating the glower element by any suitable means, such as a resistance heater located adjacent the element, to a temperature at least as high as 1000 C. and preferably at least as high as 1200 C.

During the time that the element is heated to this temperature by an external source, it is maintained out of contact with any oxygen-containing environment and connected to a source of direct current. Direct current is passed through the element and is of sufiicient magnitude to cause resistive heating of the element to a higher temperature of about 1600 or greater. By holding the element at the higher temperature for a sulficient time, usually thirty to sixty minutes, it is electrolyzed and thereafter behaves like a metallic conductor. That is, whereas in the usual ceramic glow devices the resistivity increases as the temperature falls back to room temperature, in the present instance the improved conductance obtained by following this process is retained at room temperature. For example, the room temperature resistivity of untreated glower elements is several megohm-cm. This compares with resistivity of less than 0.1 ohm-cm. obtained in elements consisting of 8 percent Y O balance zirconia. which were externally heated to 1 200 C. and then subjected to direct current flows of from 75 amps/cm. to 300 amps/cm. to raise the temperature of the elements to around 1700 C. They were held at this temperature for about 45 minutes and maintained in an oxygen free environment (commercial argon). Current densities were increased appropriately during the high temperature treatment to maintain the temperature as the resistivities dropped.

After the element has been raised to the necessary conductivity, it is placed within the sealed container where it is maintained out of contact with any oxygencontaining environment. If this procedure is followed, the generator will operate without the use of an auxiliary heater merely by causing electricity to flow through the glower element 10 vis-a-vis the electrical conductors 11.

Although the present invention has been described in connection with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A method for improving the room temperature electrical conductivity of a Nernst-type glower lamp element, which element is a ceramic body consisting essentially of zirconia and an oxide additive selected from the group consisting of from 10 to 20 mol percent calcium oxide, 7 to 52 mol percent yttria, heating said element in an oxygen-free, chemically inert, environment to a temuerature of about 1000 to 1 200 C. to render it electrically conductive, passing direct current through said heated element to resistively heat it to a temperature of at least about l600 C., holding said element at said higher temperature for a time suflicient to electrolyze said element, and cooling said element in the oxygen-free environment.

2. The method set forth in claim 1 wherein the composition of said element consists essentially of 8 to 10 mol percent yttria and the balance zirconia.

References Cited UNITED STATES PATENTS 2,170,683 8/1939 Friederich et a1 313-218 LEON D. ROSDOL, Primary Examiner.

J. D. WELSH, Assistant Examiner.

US. Cl. X.R. 313-218; 10657 

